1. Field of the Invention
The present invention is directed to detergent compositions containing specific cellulase compositions. In particular, the present invention is directed to detergent compositions containing (a) a cleaning effective amount of one or more surfactants and (b) a cellulase composition containing one or more endoglucanase (EG) type components and less than about 5 weight percent of exo-cellobiohydrolase (CBH) I type components and, preferably, less than about 5 weight percent of all CBH type components. Even more preferably, the cellulase compositions employed in the detergent compositions of this invention are free of all CBH I type components and preferably free of all CBH type components. Such detergent compositions provide improvements in softness, feel, color retention/restoration, and the like. Additionally, when such cellulase compositions contain some CBH I type components., although less than about 5 weight percent, an incremental cleaning benefit is also observed.
2. State of the Art
Cellulases are known in the art as enzymes that hydrolyze cellulose (.beta.-1,4-glucan linkages) thereby resulting in the formation of glucose, cellobiose, cellooligosaccharides, and the like. While cellulases are produced (expressed) in fungi, bacteria and the like, those produced by fungi have been given the most attention because certain fungi produce a complete cellulase system capable of degrading crystalline forms of cellulose and such cellulases can be readily produced in large quantities via fermentation procedures.
In regard to the above, Schulein, "Methods in Enzymology", 160, 25, pages 234 et seq. (1988), discloses that certain fungi produce complete cellulase systems which are comprised of several different enzyme classifications including those identified as exo-cellobiohydrolases (EC 3.2.1.91) ("CBH"), endoglucanases (EC 3.2.1.4) ("EG"), and .beta.-glucosidases (EC 3.2.1.21) ("BG"). On the other hand, some fungi are incapable of producing complete cellulase systems. Generally, these systems lack CBH components. See, for instance, Coughlan et al., Biochemistry and Genetics of Cellulose Degradation, Aubert et al., Editor, pages 11 et seq., (Academic Press, 1988); and Wood et al., Methods in Enzymology, 160, 25, pages 87 et seq., (Academic Press, New York, 1988).
Likewise, while bacterial cellulases are reported in the literature as containing little or no CBH components, there are a few cases where CBH-like components derived from bacterial cellulases have been reported to possess exo-cellobiohydrolase activity.
The fungal cellulase classifications of CBH, EG and BG can be further expanded to include multiple components within each classification. For example, multiple CBHs and EGs have been isolated from a variety of fungal sources including Trichoderma longibrachiatum which contains 2 CBHs, i.e., CBH I and CBH II, and at least 3 EGs, i.e., EG I, EG II and EG III.
The complete cellulase system comprising components from each of the CBH, EG and BG classifications is required to efficiently convert crystalline cellulose to glucose. Isolated components are far less effective, if at all, in hydrolyzing crystalline cellulose. Moreover, a synergistic relationship is observed between the cellulase components particularly if they are of different classifications. That is to say the effectiveness of a complete cellulase system is significantly greater than the sum of the contributions from the isolated components of the same classification. In this regard, it is known in the art that the EG components and CBH components synergistically interact to more efficiently degrade cellulose. See, for example, Wood, Biochem. Soc. Trans., 13, pp. 407-410 (1985).
The substrate specificity and mode of action of the different cellulase components varies significantly with classification which may account for the synergy of the combined components. For example, the current accepted mode of cellulase action is that endoglucanase components hydrolyze internal .beta.-1,4-glucosidic bonds, particularly, in regions of low crystallinity of the cellulose and exo-cellobiohydrolase components hydrolyze cellobiose from the non-reducing end of cellulose. The action of endoglucanase components greatly facilitates the action of exo-cellobiohydrolases by creating new chain ends which are recognized by exo-cellobiohydrolase components.
.beta.-Glucosidase components act only on cellooligosaccharides, e.g., cellobiose, to give glucose as the sole product. They are considered an integral part of the cellulase system because they drive the overall reaction to glucose and thereby relieve the inhibitory effects of cellobiose on CBH and EG components.
On the other hand, cellulases are also known in the art to be useful in detergent compositions for the purposes of enhancing the cleaning ability of the composition, for use as a softening agent, and for improving the feel of cotton fabrics, and the like. While the exact mechanism by which cellulase compositions soften garments is not fully understood, softening and color restoration properties of cellulase have been attributed to alkaline endoglucanase components in cellulase compositions. Thus, for instance, International Application Publication No. WO 89/09259 discloses that detergent compositions containing a cellulase composition enriched in a specified alkaline endoglucanase component impart color restoration and improved softening to treated garments as compared to cellulase compositions not enriched in such a component. Additionally, the use of such alkaline endoglucanase components in detergent compositions complements the pH requirements of the detergent composition. The endoglucanase component of this reference is defined as one exhibiting maximal activity at an alkaline pH of 7.5 to 10 and which has defined activity criteria on carboxymethylcellulose and Avicel.
On the other hand, cellulase compositions are known in the art to degrade cotton-containing fabrics (see, for example, Suzuki et al., U.S. Pat. No. 4,822,516) which degradation is evidenced by reduced strength loss in the fabric. In turn, such strength loss accounts, in part, for the reluctance to the use of cellulase compositions in commercial detergent applications.
Accordingly, in view of the above, cellulase compositions containing one or more endoglucanase components which also provide reduced strength loss for cotton-containing fabrics as compared to a complete cellulase system would be particularly advantageous for use in detergent compositions.